(1) Field of the Invention
This invention relates to a warp tension regulating and warp feed apparatus in a circular loom.
(2) Description of the Prior Art
As the loom for weaving a tubular fabric, a circular loom has been known for many years. This circular loom however, involves various problems. For example, the structures of the shed forming mechanism and filling mechanism are more complicated than in the conventional power loom, and the actually aplicable fabric structure is limited to a plain weave structure. Furthermore, the densitites of the warps and wefts constituting a woven fabric are coarser than in a woven fabric made by the conventional power loom. Because of these problems, the known circular looms have hardly been put into practical use.
Bags made from woven fabric of a plain weave structure utilizing tapes of synthetic resins, such as polypropylene, polyethylene resins or synthetic resin strands, such as multifilament yarns or cords of synthetic resins, as warps and wefts have been broadly used for transportation and storage of granules, such as grains, sugar fertilizers and synthetic resin pellets. This is because these bags are strong and light in weight. For manufacturing these bags, a single fabric of a plain weave structure or a tubular fabric of a plain weave structure is produced by known power looms, and then, this fabric is cut into pieces of fabric and the pieces of fabric are sewed to form the bags. Warps and wefts used for formation of these bags are much thicker than yarns used for formation of ordinary clothing fabrics, and therefore, the weave densities of these warps and wefts are very coarse. Accordingly utilization of a circular loom for producing these bags has been taken into consideration. Furthermore, a tubular fabric of a more uniform texture can be made by a circular loom than by the conventional power loom, and in case of a circular loom, since shuttles are moved in one direction, the weaving speed can be increased. Therefore, various attempts have been made to utilize circular looms in not only Japan, but, also, other industrially advanced countries. As a typical instance, there can be mentioned a circular loom previously proposed by us, for example, the circular loom disclosed by U.S. Pat. No. 3,871,413, or a circular loom which has been manufactured and sold by the British Company, Fairbairn Lawson Machinery Ltd. In these circular looms, many warps are guided to a plurality of shed forming mechanisms arranged along an annular shuttle guide member and shuttles travel in one direction along this annular shuttle guide member, prior to arrival of the shuttles, sheds are sequentially formed by the shed forming mechanisms and the shuttles travel and pass through these sheds. Then, the sheds are closed, and prior to arrival of subsequent shuttles, the positions of the shed-forming warps are reversed and sheds are sequentially formed. The shuttles are then inserted and passed through these sheds to form a plain weave structure. A so-formed tubular fabric of a plain weave structure is then taken out from the circular loom. As can be understood from these weaving procedures, in these conventional circular looms, due to the shed forming operation during the weaving process, it is almost impossible to avoid the occurence of tension variation on the respective warps. In these variations if warp tensions are not controlled or compensated for an unbalance is created among tensions on the respective warps. If this unbalance is increased, formation of sheds becomes difficult, resulting in occurence of mispicks. As means for preventing occurrence of such defects, there has been adopted a method in which variations of warp tensions are moderated by using dancing levers. For example, one end of each dancing lever is pivoted on a machine frame and a yarn guide for passing a warp therethrough is formed on the other end of each dancing lever, and a resilient pulling member, such as a spring, is connected to each dancing lever to impart a turning moment coping with the tension of the warp passing through the yarn guide. Accordingly, each dancing lever is allowed to swing under the action of the resilient pulling member according to a variation of the tension on the corresponding warp, and the variation of the warp tension is absorbed and compensated for by this swinging movement of the dancing lever. However, since a dancing lever of this type is allowed to swing only within a certain limited range for absorption of variations of the warp tension, a tension variation of a small amplitude can be effectively absorbed, but a tension variation of a large amplitude cannot completely be absorbed. Generally, in a circular loom, variations of tensions on warps have a large amplitude, and therefore, conventional dancing levers of the above-mentioned type can not be satisfactorily used in the circular loom.